74 BACKWATER CURVES — INTRODUCTORY 



The computations in the table are explained by the column headings. The 

 column headed " x " is obtained directly as indicated by the equation above, 

 and represents the distance from the arbitrary origin which happens to be 

 11.49 miles upstream from the dam. A larger number of values of z could 

 have been included in the table if more points on the curve had been needed. 

 On the other hand, as few values could have been used as desired. There is 

 no necessity that the intervals between computed values be small. 



PROBLEMS 



603. Assume that the channel of the illustrative example has a sudden drop-off 

 instead of a dam, all other conditions remaining the same. Determine the backwater 

 curve, and plot it to an exaggerated vertical scale. 



604. Water flows from under a gate in a wide rectangular channel. The bottom of 

 the channel is level to a point 1,000 feet downstream from the gate, where it has a 

 sudden drop-off. The bottom of the gate is 5 feet above the floor of the flume and 

 the depth of the water upstream is 20 feet. Assuming that the depth at the vena 

 contracta is 3.9 feet and that n = 0.013, determine the water-surface profile from the 

 gate to the drop-off. 



605. Water spills over a levee by-pass and flows down a smooth concrete apron 

 built on a slope of 12 horizontal to 1 vertical. What will be the depth of the water 

 100 feet downstream from the crest, if the head on the crest is 3 feet, and the friction 

 losses up to the crest may be neglected? 



